Enrichment Effect Of Carbon, Nitrogen, Phosphorus And Heavy Metals In Sediment Under Plant Communities In River

To research the accumulation mechanism of organic carbon (Corg), total nitrogen (TN), total phosphorus (TP) and heavy metals (As, Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn) in sediment under plant communities in river, we selected three single dominant communities of Scirpus planiculmis and Sparganium stoloniferum respectively in each habitat (Shoal area and Shallow water area) in Suo River, a tributary of Huai River, and collected surface layer (0-10 cm), middle layer (10-20 cm) and sublayer (20-30 cm) sediment respectively under the plant communities and CK (blank control). We verified the enrichment effect of Corg, TN, TP and heavy metals in each layer sediment under plant communities using T-test for independent samples, and calculated each element’s relative enrichment index (REI), and then used partial least squares regression (PLSR) to analyze the influence factors to element’s REI.The results showed that Corg (77.2), TN (51.0), Cd (86.0), Cr (16.6), Pb (12.2) and Zn (48.1) significantly enriched in surface sediment under Scirpus planiculmis (REI in brackets, the same below) and Corg (92.7), TN (55.6), As (28.2), Cd (86.1), Cr (12.1), Hg (63.4), Ni (42.0), Pb (17.4) and Zn (53.5) significantly enriched in surface sediment under Sparganium stoloniferum. While only Hg (48.3) significantly enriched in middle layer sediment under Scirpus planiculmis, and only Cr (15.7) and Pb (13.9) significantly enriched in sublayer sediment under Scirpus planiculmis.In conclusion, Corg, TN, Cd, Cr, Hg, Pb and Zn significantly enriched in sediment of 0-30 cm depth under Scirpus planiculmis, and Corg, TN, As, Cd, Cr, Hg, Ni, Pb and Zn significantly enriched in sediment of 0-30 cm depth under Sparganium stoloniferum plant communities. And the enrichment effect occurred mainly in the surface sediment.And for the surface sediment, the main influence factors to REIs were elements’ background values in sediment, successively followed by plant species, habitat type and sediment texture. Specifically, elements’ REIs were positively correlated to elements’ background values in sediment. Corg, TN, Cd, Ni, Pb and Zn enriched more in surface sediment under Scirpus planiculmis, while As, Cr and Hg enriched more under Sparganium stoloniferum. Relative to the Shoal area, elements, especially TN, Cr and Ni enriched more in sediment of Shallow water area. While the influence of sediment texture to REIs is relatively small, only As’ REI was positively correlated to the particle size of sediment.For the middle layer sediment, the main influence factors to Hg’s REI were plant species, successively followed by Hg’s background value in sediment, habitat type and sediment texture. Specifically, Hg enriched more in middle layer sediment under Scirpus planiculmis than Sparganium stoloniferum. Hg’s REI was positively correlated to Hg’s background value in sediment. Relative to the Shoal area, Hg enriched more in sediment of Shallow water area. Hg’s REI was negatively correlated to the particle size of sediment.For the sublayer sediment, the main influence factor to Cr’s REI was Cr’s background value in sediment, successively followed by habitat type and plant species. Specifically, Cr’s REI was positively correlated to Cr’s background values in sediment. Cr enriched more in sediment of Shallow water area than Shoal area. And Cr enriched more in sublayer sediment under Sparganium stoloniferum than Scirpus planiculmis. While the main influence factor to Pb’s REI was Pb’s background value in sediment, successively followed by plant species. Specifically, Pb’s REI was positively correlated to Pb’s background value in sediment. And Pb enriched more in sublayer sediment under Scirpus planiculmis than Sparganium stoloniferum.Overall, the main influence factors to the elements’ REIs were the elements’ background values in sediment, successively followed by plant species, habitat type and sediment texture.The research results of this paper can provide certain reference for the polluted river’s ecological restoration. Planting local dominant species in polluted river helps carbon, nutrient elements and some heavy metals in river ecosystem transfer into the sediment, especially into surface sediment, under the plant communities. The main driving forces may be plants’ interception of particulate matter and nutrients in water, and the decomposition and mineralization of plant litter and died root. Maybe Scirpus planiculmis can absorb Cd, Cr, Hg, Pb and Zn and Sparganium stoloniferum can absorb As, Cd, Cr, Hg, Ni, Pb and Zn, which needs to be validated in further research.